FIG. 1 shows a typical magnetic disk drive 10. As shown in FIG. 1, the disk drive 10 includes a disk stack of one or more magnetic disks 12 rotatable about a spindle 14. The spindle 14 is driven by a spindle motor 16, for example, a DC brushless motor. Data is written onto a magnetic disk by one or more associated read/write head(s) 18, and data is read back using the same read/write head(s) 18. The read/write head(s) 18 is/are attached to a suspension arm 20. The suspension arm 20 forms part of an actuator 22. The actuator 22 is pivotable about a pivot 24 and is driven by a voice coil motor (VCM) 26 disposed on an arm opposite the suspension arm 20. As can be seen from FIG. 1, the VCM 26 actuates the actuator 22 such that a read/write head 18 moves across a surface of an associated magnetic disk 12 in a substantially radial manner. Near the outer edge of the disk stack is a load/unload ramp 30. At a free end of each suspension arm 20 is a tab 28 extending beyond the read/write head(s) 18. The tab 28 is operable to engage with the load/unload ramp 30 during parking of the actuator 22.
In normal use, power is supplied from the mains to the disk drive 10, and the position and velocity of both the actuator 22 and read/write head(s) 18 are determinable from the servo information stored on the associated magnetic disk 12 surface. During a proper shut down operation, power is still available for a disk drive controller to move the actuator 22 back to its parking position. In the parked position, each tab 28 at the end of the suspension arm 20 is made to ride up an inclined surface of the associated load/unload ramp 30 such that the read/write head 18 is lifted up from the surface of the associated magnetic disk 12; this operation is called “unloading” of the read/write head(s) 18. When the disk drive 10 is powered up after a shut-down operation, the actuator 22 is moved from the parked position and the read/write head 18 is “loaded” onto the associated magnetic disk 12 surface. Unloading of the read/write head(s) 18 would reduce wear and tear on both a slider carrying each read/write head 18 and the associated magnetic disk surface.
During normal operation, the relative speed between a read/write head 18 and the associated disk surface creates an air cushion to lift the read/write head 18 a small height from the disk surface. Thus, each read/write head 18 relatively “flies” above the associated disk surface. In the event of a power interruption, the relative speed between the read/write head and the disk surface may not be sufficient to create an air cushion to fly the read/write head above the disk surface. Immediately after such a power interruption, the spindle motor 16 continues to rotate due to the momentum stored in the rotating magnetic disk(s) 12. During this transient period, the spindle motor 16 acts as a generator and sinusoidal back electro-motive force (BEMF) is generated across each winding in the spindle motor 16. Therefore, it is desirable to tap the motor BEMF voltages for parking the actuator 22 and unload the read/write head(s) 18 whilst the magnetic disk(s) 12 is/are still spinning.
Attempts have been made to tap the power from the BEMF to bring the actuator to its parking position during this transient period. FIG. 2 illustrates a typical disk driver system 50. As shown in FIG. 2, the system 50 includes a 3-phase DC spindle motor 16, a commutation circuit 60 consisting of six power transistors UA, UB, UC, LA, LB, LC; a bridge rectifier 80 consisting of six Schottky diodes; and a VCM 26. Not shown in FIG. 2 is a motor driver 70. During normal operation, the motor driver 70 controls the commutation circuit 60 to regulate the spindle motor 16 in one direction by turning ON the relevant power transistor UA, UB . . . LB, LC coupled to windings A, B and C in a cyclical manner. After a power interruption, the momentum in the rotating disks 12 causes the spindle motor 16 to generate sinusoidal BEMF voltages across each winding A, B, C. The BEMF voltages are passively rectified to supply power to the VCM 26 for parking the actuator 22. Capacitor 90 is used to store any excess power, which may be required by the VCM 26 to complete parking of the actuator 22.
Attempts have been made to tap the power from the motor BEMF. One approach given is a driver system 100 shown in FIG. 3. As shown in FIG. 3, the system 100 includes a 3-phase motor 116, a motor driver 110 consisting of a H-bridge of 6 power transistors UA, UB, UC, LA, LB, LC; a commutator circuit 114, a decoder and latch circuit 118, a VCM 126; a FET isolation circuit 120 and a VCM control circuit 124. The commutator circuit 114 consists of three comparators CPA, CPB, CPC. Each of the comparator CPA, CPB, CPC is coupled across the respective motor winding A, B, C. After power interruption, the mains supply Vcc is uncoupled by the isolation circuit 120 and the output of the commutator circuit 114 is decoded and latched by the circuit 118 such that the relevant power transistor UA, UB LB, LC is sequentially turned ON to allow the BEMF across each winding A, B, C to pass through to power the VCM 126. The VCM control circuit 124 drives the VCM 126 in one direction or another in accordance with the desired direction of the read/write head 18.